In the marine environment the generation and discharge of contaminated wastewaters need to be controlled to avoid polluting said environment. In particular, sea-going vessels must discharge ballast water, graywater from laundry and dishwashing etc., and blackwater sewage directly into a body of water, such as an ocean. In addition, during sediment dredging operations excess waters are generated that can be contaminated if the sediments being excavated contain pollutants such as heavy metals or problematic organic compounds.
Current strategies to control these discharges vary from location to location, but in general wastewaters from sea-going vessels are managed by either discharging said waters in deeper ocean waters away from the coastline, installing treatment systems on-board the offending sea-going vessel, or storing said waters on the offending vessel and pumping said waters to a treatment or transfer facility at the docking port. Wastewaters generated during dredging operations, if such waters are contaminated, are, in almost all cases, pumped to an on-shore impoundment or treatment facility for management.
This invention includes methods and processes for managing such waters using a mobile floating water treatment vessel with membrane filtration treatment technology capable of achieving highly efficient degrees of treatment that can readily address the primary concerns associated with marine wastewater discharges. This can be accomplished without the need for on-board or on-shore treatment systems. As will be readily apparent upon further elaboration of these marine wastewater discharges and the water treatment approach associated with this invention, the development of such a mobile treatment system lends itself not only to the treatment of ballast water, graywaters, blackwaters, and contaminated dredge waters, but also to the treatment or pretreatment of raw marine water for potable water use or near-shore industrial discharges should such treatment be necessary.
Ballast Water
Ballast in the form of water is taken on board vessels to reduce the stresses in the hull of the ship, to provide for transverse stability, to aid propulsion by controlling submergence of the propeller, and to aid in maneuverability by submerging the rudder and reducing the amount of exposed hull surface (free board and windage) and to compensate for weight loss from fuel and water consumption. Dry bulk carriers, ore carriers, tankers, container ships, general cargo vessels, passenger vessels, and military vessels all take on ballast water either in port or during a voyage. Most ships deballast (discharge ballast water) during cargo loading operations and take on ballast water during cargo unloading operations.
As a result of ballasting and deballasting operations, oceangoing vessels can be expected to transport marine organisms, contained in the ballast water, from any port in the world to any other port in the world. The development of effective methods to control the transport and/or release of nuisance organisms that are found in ballast water is a problem facing the international maritime community. When such nuisance organisms (mollusks, crustaceans, worms, seaweed, algae, fungi, and protozoa) present in the ballast water (taken on board from a foreign port) are introduced into a new ecosystem (by discharging of the ballast water into a secondary port""s coastal environment), there are often no natural predators for these organisms (commonly referred to as aquatic nuisance species). Introducing aquatic nuisance species into new environments can have serious environmental consequences. The threat of non-indigenous species introduced through ship deballasting is a worldwide problem. Ships deballast in ports everywhere in the world impacting local fishing industries and the ecology (National Research Council, 1996. Stemming the Tide: Controlling Introductions of Nonindigenous Species by Ships"" Ballast Water, National Academy Press, Washington, D.C.).
At the present time, the most common strategy for controlling foreign species present in ballast water is the ballast water exchange process. In this process cargo vessels unload ballast water (taken on board at a local port after discharging cargo) into the open ocean and exchange the discharged ballast water with mid-ocean seawater (International Maritime Organization, 1998. Guidelines for the Control and Management of Ships"" Ballast Water to Minimize the Transfer of Harmful Aquatic Organisms and Pathogens, London, 1998). While currently the standard recommended practice, this method is generally not considered to be very effective in controlling aquatic nuisance species because 1) organisms often continue to survive in the sediment and residual water in ballast tanks; 2) the process can take 6 to 24 hours and subject a vessel to instability during turbulent weather, resulting in serious safety issues; and 3) mid-ocean ballast water exchange can also stress the structural integrity of cargo vessels, particularly under turbulent weather conditions (Motor Ship, 2000, Ballast Water Management: Balancing Green Issues with Safety, Motor Ship, May 2000).
Other technologies being proposed or investigated for treating ballast water include particle filtration processes, gravity processes (sedimentation, flotation, and centrifugation), thermal processes (pasteurization at 60xc2x0 C. to kill organisms), electromagnetic radiation (UV lamps), chemical treatment (including chlorination, ozonation, pH adjustment, deoxygenation, and salinity adjustment), and gaseous sterilization (using the exhaust gases from the ship""s engine to kill organisms) (National Research Council, 1996. Stemming the Tide: Controlling Introductions of Nonindigenous Species by Ships"" Ballast Water. National Academy Press. Washington, D.C.).
A number of recent U.S. patents have been issued on proposed ballast water treatment approaches. Gill, Method for Controlling Zebra Mussels in Ship Ballast Tanks, U.S. Pat. No. 5,128,050, Jul. 7, 1992, proposes to control zebra mussels or its larvae by introducing the chemical didecyl dimethyl ammonia halide into ballast water tanks. Eguisa and Fukuyo, Method for Destroying Cyst of Noxious Plankton, U.S. Pat. No. 5,256,423, Oct. 26, 1993, propose a strategy to control the cyst of noxious plankton by introducing hydrogen peroxide. Sherman, Ballast Water Treatment System, U.S. Pat. No. 5,816,181, Oct. 6, 1998, proposes to pump the ballast water through heat exchangers on board a vessel using the waste energy from the propulsion system of the vessel as the heat source. Browning, Method and Apparatus for Killing Microorganisms in Ship Ballast Water, U.S. Pat. No. 5,932,112, Aug. 3, 1999, proposes a deoxygenation approach designed to suffocate the organisms contained in the ballast water. Rodden, Ballast Water Treatment, U.S. Pat. No. 6,125,778, Oct. 3, 2000, proposes the treatment of ballast water with ozone while the vessel is in transit between ports. Rodden describes several proposed methods for contacting the ballast water with the ozone to effect this treatment approach.
While all of the above methods offer some potential treatment options, the introduction of chemical reagents into ballast water tanks to kill nuisance organisms could have adverse impacts on receiving waters when the ballast water is discharged. Heat treatment and deoxygenation strategies may be possible in theory, but many microbes are capable of overcoming such environments through spore formation and anaerobic activity. Ultraviolet radiation is untested at such high flow rates and the effectiveness of these approaches with liquids containing high levels of suspended solids are questionable. In short, none of the currently proposed strategies offers solutions that appear practical. In addition, the focus of essentially all the aforementioned treatment applications has been to consider the siting of such treatment systems on-board the offending vessel. Siting these facilities on-board the offending vessel means that all existing vessels must be retrofitted to install the necessary equipment and all new vessels must be designed to have the necessary equipment installed during fabrication. The cost of retrofitting existing vessels and installing treatment equipment on all new vessels will be extremely high.
Graywater and Blackwater
Graywater as defined by the International Maritime Organization means drainage from dishwashers, showers, laundries, baths, washbasins and galleys. Blackwater is comprised primarily of wastewater from toilets, urinals, and medical facilities. Graywater discharges in the past have not been subjected to permitting or regulatory requirements, however, with the proliferation of cruise line trips in recent years, local, state, and national environmental agencies are in the process of developing requirements for managing these discharges. Blackwater treatment utilizing marine sanitation devices is already required under U.S. Federal law. These sanitation devices usually encompass either chemical and/or biological treatment.
While blackwaters can be treated to reduce the oxygen demand and suspended solids content of such waters using conventional sewage treatment processes, incorporating such processes in a compact manner that can manage shipboard wastes requires more innovative approaches. A number of U.S. patents have been issued for systems designed for the treatment of shipboard-generated graywaters and blackwaters.
Svanteson, Method of processing Waste on Ships and the Like and Arrangement for Carrying Out the Method, U.S. Pat. No. 4,038,184, Jul. 26, 1977, introduced a method for treating shipboard blackwaters using a rotating drum, with knife-edged elements to shred the solid materials in the waste stream, and with hot air introduced into said drum for the purpose of evaporating the liquid waste, leaving only solids for collection and disposal. Svanteson proposed the use of waste heat from the ship""s machinery as the energy source for the hot air used in the evaporation process. Alig, Shipboard Blackwater Physical/Chemical Treatment System, U.S. Pat. No. 4,197,200, Apr. 8, 1980, proposed the use of ozonation for the disinfection of shipboard blackwater after the removal of solids using a screening device and the pumping of the collected solids to the ship""s boilers for incineration. Rummier, Waste Treatment System, U.S. Pat. No. 6,156,192, Dec. 5, 2000, proposed a waste treatment system for blackwaters and graywaters generated in household, commercial, industrial environments, and shipboard environments that makes use of liquid-solid separation processes, incineration processes using microwave technology, and disinfection processes using oxidants and ultraviolet radiation treatment.
Miller et al, Fluid Treatment Process Using Dynamic Microfiltration and Ultrafiltration, U.S. Pat. No. 5,374,356, Dec. 20, 1994, proposed a method for recycling shipboard graywaters using membrane filtration technology. Miller""s invention incorporates a two-stage process requiring microfiltration and ultrafiltration. In this two-staged process, as the graywater is filtered through each stage, the influent is divided into a filtrate or permeate stream and concentrate streams. Miller employs in his invention dynamic microfiltration and cross-flow ultrafiltration processes. Dynamic filtration is a process where the membrane filter medium is in motion to induce high shear forces on the membrane. This assists in maintaining a filter-free medium, free from plugging or fouling.
Miller follows his ultrafiltration process with ozonation and ultraviolet light radiation to both sterilize the graywater and oxidize organic compounds. Miller""s primary purpose is to generate a water stream that can be recycled. While the filtrate is intended for reuse, the concentrate stream generated during the microfiltration and ultrafiltration operation must be discharged to shore-side treatment facilities. Miller, Fluid Treatment Process, U.S. Pat. No. 5,578,213, Nov. 26, 1996, presents modifications to his 1994 invention by introducing pretreatment processes for free oil removal and post-treatment adsorbent bed systems to remove organic and inorganic contaminants such as chlorine and metal ions and eliminating the cross-flow ultrafiltration step in his 1994 invention.
While there has and continues to be work undertaken to develop more cost effective technologies for managing shipboard wastewaters, strategies to manage graywater or blackwater have exclusively been limited to the establishment of treatment systems either on-board the offending vessel or strategies that require the discharge of these wastewaters to a land-based treatment system.
Dredge Water
It is the nature of current subsurface dredging or subsurface sediment excavation processes that during said excavation, particulate matter will be dispersed into the water column. This occurs because dredging to extract and remove bottom sediments involves mechanically raking, grabbing, penetrating, cutting, or hydraulically scouring the bottom of the waterway to dislodge sediment. This is a special problem when the dredge site contains highly contaminated materials that must be removed without dispersing the sediments and contaminating alternate locations. Bottom sediments disturbed by dredging operations, but not removed from the water body, pose several environmental problems. If the sediments are contaminated, the resuspension of particles provides the means for contaminants to migrate from their original source to new locations, impacting marine life in these areas and ultimately the ecosystem and food chain.
Of particular concern is the resuspension of fine clay and organic sediment particles (micron- and submicron-sized). Such particles tend to concentrate contaminants due to their high absorptive properties and the large surface areas that are cumulatively available in this very small size range. In addition to sediment toxicity problems, excessive particulate resuspension in environmentally sensitive areas results in visible turbidity, which may inhibit fish migration or reproductive patterns, impair fish gills, or cover larvae, eggs or bottom-feeding invertebrates (United States Environmental Protection Agency, 1994, Assessment and Remediation of Contaminated Sediments (ARCS) Program, Remediation Guidance Document, USEPA 905-B94-003, October 1994).
Current methods of dredging can be divided into two general categories. They include mechanical dredging and hydraulic dredging. The fundamental difference between these categories is in the form in which the sediments are removed. Mechanical dredges remove the sediments directly with clamshell-type buckets. The operation consists of lowering the bucket with a crane to the bottom of the waterway, scooping or extracting the sediment, and bringing the sediment to the surface for disposal (typically in a dredge barge). Hydraulic dredges, sometimes referred to as vacuum dredges, are designed to vacuum-up bottom sediments. Unless the sediments are very loose, vacuum dredges require cutter heads or alternative means to dislodge the dredge material so that the sediment can be vacuumed into the dredge head.
To effectively collect contaminated particles suspended during the dredging process, it is necessary to collect both the particulates and a given quantity of water, associated with the water column into which said particles are dispersed. When hydraulic dredges are used to excavate contaminated sediments, the sediment and the vacuumed water are almost always pumped to an on-shore impoundment or treatment facility where the sediment is separated from the water and the excess water is treated. Mechanical clamshell-type dredges typically excavate within confined silt curtains and do not manage excess waters and particulates, although the authors of this patent have recently submitted a patent application (provisional Patent Serial No. 60/190,809 filed Mar. 21, 2000) that describes a mechanical clamshell bucket system that is housed in a pressure-controlled enclosure that collects and contains dispersed particulates generated during the clamshell bucket excavation process and pumps the particulates and water contained in the housing to a treatment facility; and have also submitted a second patent application (provisional patent Serial No. , filed on Mar. 9, 2001) that describes a mobile barrier vessel in which sheet piles along with a drape are lowered from the vessel to the subsurface to create a sealed control zone in which a clamshell bucket can excavate contaminated sediment, while the liquid in the control zone is pumped to a treatment facility.
While mechanical clamshell-type dredges typically do not draw water under vacuum during the excavation process, they do collect and deposit excess water into the dredge barge. If the excess water is extracted from the barge, it must be treated prior to discharge. Otherwise the water must be transported and disposed of with the contaminated sediments.
In both hydraulic and mechanical dredging operations, the siting and permitting of on-shore impoundment and/or treatment facilities to manage contaminated dredge waters are major problems when the dredging of contaminated sites are being planned.
It is an object of the present invention to provide a mobile, floating treatment vessel to treat contaminated water generated in the marine environment with a membrane filtration treatment system to enable the discharge of this treated water back into the ambient environment.
It is also an object of this invention to collect ballast water from vessels entering a port or harbor area.
It is a further object of the invention to provide a method for treating ballast water to remove essentially all aquatic nuisance organisms from the ballast water using membrane filtration technology.
It is a further object of the invention to use polymeric membranes capable of micro and ultrafiltration as a ballast water treatment method.
It is a further object of the invention to use either pressurized or immersed vacuum driven hollow fiber membrane treatment systems to treat the ballast water.
It is a further object of the invention to provide such a ballast water treatment system on-board a self-contained treatment vessel.
It is a further object for this self contained ballast water treatment vessel to contain the necessary equipment and treatment operation to pump the ballast water, recirculate and treat the retentate stream, collect, stabilize, and treat solids and organisms removed from the ballast water, and clean and maintain the filters used in the process.
It is a further object of the invention to discharge treated ballast water directly back into the port ambient water environment.
It is a further object of the invention to convert the collected solids generated in the ballast water treatment process system to a stabilized form prior to disposal.
It is a further object of the invention to collect ballast water from incoming vessels, which require treatment, by direct discharge into the ballast water treatment vessel or by discharge into intermediate storage barges available to store the ballast water until such time as treatment may be effected.
It is also an object of this invention to collect dredge water from the discharge of dredging operations designed to remove sediments from the bottom of waterways.
It is a further object of the invention to provide a method for treating dredge water to remove essentially all suspended solids from the dredge water using membrane filtration technology and provide pre-or post-treatment to remove soluble metals and/or organic compounds, if necessary.
It is a further object of the invention to use polymeric membranes capable of micro and ultrafiltration as a dredge water treatment method.
It is a further object of the invention to use either pressurized or immersed vacuum A driven hollow fiber membrane treatment systems to treat the dredge water.
It is a further object of the invention to provide such a dredge water treatment system on-board a self-contained treatment vessel.
It is a further object for this self contained water treatment vessel to contain the necessary equipment and treatment operation to pump the dredge water, recirculate and treat the retentate stream, collect, stabilize, and treat solids removed from the dredge water, and clean and maintain the filters used in the process.
It is a further object of the invention to discharge treated dredge water directly back into the ambient water environment.
It is a further object of the invention to convert the collected solids generated in the dredge water treatment process system to a stabilized form prior to disposal.
It is a further object of the invention to collect dredge water from the dredging operations by direct discharge into the dredge water treatment vessel or by discharge into intermediate storage barges available to store the dredge water until such time as treatment may be effected.
It is also an object of this invention to collect graywater or blackwater from vessels entering a port or harbor area or at a designation location.
It is a further object of the invention to provide a method for treating graywater or blackwater to remove essentially all suspended solids and a large fraction of organic matter, if necessary, using membrane filtration technology.
It is a further object of the invention to use polymeric membranes capable of micro and ultrafiltration as a graywater or blackwater treatment method.
It is a further object of the invention to use either pressurized or immersed vacuum driven hollow fiber membrane treatment systems to treat the graywater or blackwater.
It is a further object of the invention to provide such a graywater or blackwater treatment system on-board a self-contained treatment vessel.
It is a further object for this self contained water treatment vessel to contain the necessary equipment and treatment operation to pump the graywater or blackwater, recirculate and treat the retentate stream, collect, stabilize, and treat solids removed from the graywater or blackwater, and biologically treat such water, if necessary, and clean and maintain the filters used in the process.
It is a further object of the invention to discharge treated graywater or blackwater directly back into the ambient water environment.
It is a further object of the invention to convert the collected solids generated in the graywater or blackwater treatment process system to a stabilized form prior to disposal.
It is a further object of the invention to collect graywater and blackwater from incoming vessels, which require treatment, by direct discharge into the graywater or blackwater treatment vessel or by discharge into intermediate storage barges available to store these waters until such time as treatment may be effected.
It is also an object of the present invention to improve over the disadvantages of the prior art.
In keeping with these and other objects of the invention, which will become apparent, a method is provided for treating marine waters and wastewaters generated on or near the marine environment by filtering such waters through membrane filters capable of removing particulate matter including organisms in the micron and submicron range (microfiltration and ultrafiltration), discharging the permeate (clean water) back into the ambient environment, and concentrating and disposing of solid materials separated in the process. While the process described herein can be placed on-shore or on offending vessels, in keeping with the object of the invention, the treatment process as envisioned is part of a self-contained mobile treatment vessel. Such vessels can be employed at local ports, harbors, and coastal areas to accept discharges from vessels or operations that generate contaminated waters, thereby eliminating the need for an on-shore or shipboard treatment systems. Such vessels can also complement the shipboard operations by accepting portions of the waste stream not adequately handled or treated on board the offending vessel. Such a treatment vessel has direct applicability but is not limited to the treatment of ballast water, shipboard wastewaters such as graywaters and blackwaters, or dredge water.
This invention therefore includes a preferred embodiment for a mobile treatment vessel with a micro- or ultra-filtration membrane treatment system for micron and submicron sized particulate removal. Such a vessel and treatment system has not been previously applied for the treatment of ballast waters or dredge waters. Although membrane treatment systems are being considered for the treatment of shipboard wastewaters such as graywater or blackwater, such treatment systems have not been applied on a self-contained mobile treatment vessel which receives and treats contaminated water from a separate location, prior to discharging the treated water into an ambient marine environment. The treatment system of this micro or ultrafiltration membrane treatment embodiment is a multistage treatment system. The first stage includes flow equalization and pretreatment. This stage is intended to equalize the flow and to provide preliminary solids removal and, if necessary, oily water separation. The second stage includes the membrane system. This stage is designed to remove very fine micron and submicron-sized particles remaining in the water. If needed, post-treatment could be included in subsequent stages to remove residual soluble contaminants in the effluent stream using processes such as activated carbon adsorption, chemical oxidation, or ultraviolet radiation processes.
The main component of the system is the membrane filtration process.
Commercially available membrane filters act as barriers that can be used to separate particulate and dissolved components in both liquid and gaseous streams. The particular focus of the treatment proposed in this invention is separation of particles in the microfiltration (xcx9c0.1 to 10 microns) and the ultrafiltration (xcx9c0.01 to 0.1 micron) range.
There are presently two major types of commercially available microfiltration and ultrafiltration systems. These are polymeric and ceramic systems. These two systems are typically categorized, with respect to the supporting membrane module or configuration, as hollow fiber polymerics, tubular polymerics, spiral wound polymerics, plate polymerics, tubular ceramics, or dense-pack ceramics. Other membrane configurations or modifications of existing configurations, such as flat membrane systems, rotary cylinders, and rotating disc modules are also in use and new configurations are in continual development. The inventors, having tested both ceramic and polymeric systems, have found polymeric low pressure or vacuum-driven hollow fiber membrane systems to be the preferred system from a cost and effectiveness viewpoint for the subject application.
Most microfiltration and ultrafiltration systems in operation at the present time utilize positive pressure as a driving force to pass liquids through the membrane. Pressurized systems are typically operated in a dead-end mode or in a cross-flow mode. In a dead-end mode, all of the incoming raw water, with the exception of a relatively small retentate stream, sometimes referred to as a blowdown stream, is passed through the membrane. The small retentate stream is wasted to control solids buildup. In a cross-flow mode the feed is pumped tangentially to the membrane surface. In such an operation, one stream enters a membrane module (the feed stream) and two streams exit (a relatively large recirculation stream and the permeate stream). The cross-flow stream induces a shearing action on the membrane, and hence cleaning which leads to reduced particulate fouling or caking and a higher average flux rate than a dead-end operation. In this system, a retentate or blowdown stream is extracted from the recirculation stream to control solids buildup. Dead-end pressurized systems typically operate under lower transmembrane pressures than cross-flow systems. An alternative to dead-end or cross-flow operation is dynamic microfiltration. Dynamic microfiltration is a positively pressurized operation in which the filter medium is moved (typically rotated) at sufficient speed relative to the fluid stream to produce sufficient shear forces to maintain a free filter surface for extended periods of time. While dead end, cross flow, or dynamic microfiltration membrane systems are suitable for use in the subject invention, the preferred embodiment of this invention is a system that operates under low pressure. A dead-end system, which typically operates under a positive transmembrane pressures that are less than approximately 30 pounds per square inch, and is comprised of hollow fiber membranes, is a preferred system for use on a self-contained water treatment vessel.
In recent years, immersed or submerged vacuum-driven hollow fiber membranes have been introduced commercially. An immersed hollow fiber membrane filter operating under low negative pressure is a polymeric filter that achieves filtration by drawing water through a thin fiber (membrane) surface into the hollow annular inner core of the fiber. Permeated water is transported through the inner core to a common header pipe where it is discharged. To improve flux rates and reduce fouling, compressed air is typically introduced at the bottom of a fiber module to agitate the fibers and induce tangential shear forces adjacent to the membrane, thereby preventing solids buildup on the individual fibers. An immersed hollow fiber membrane system, which typically operates under very low negative transmembrane pressures of less than approximately 10 pounds per square inch, is a preferred system for use on a self-contained water treatment vessel.
In both positively pressurized and vacuum driven membrane systems a gradual solids buildup will occur in the recirculation or retentate stream and periodic retentate stream wastage in both types of systems is necessary as part of the operational process to limit the influent solids concentrations to the filters. In both systems backpulsing and interim cleaning of filters is also necessary. Chemical treatments are available (oxidizing agents, alkalis and acids) to periodically backpulse and clean the membranes to restore their flux rates should fouling occur.
To implement a membrane filtration strategy for the referenced applications, the membrane filtration embodiment of the subject invention provides for the use of a xe2x80x9cself-contained water treatment vessel,xe2x80x9d designed with water storage and equalization capacity, solids treatment and handling, and biological treatment, if needed. In essence, depending on the particular application, the invention is capable of acting as a ballast water treatment vessel, a blackwater, a graywater, or a dredge water treatment vessel, or any combination of the above.
In an embodiment for ballast water treatment of contaminated ship-board ballast water, the treatment vessel(s) would be located in, or in the vicinity of, the incoming port facility. At such a location, two operating scenarios are possible with the ballast treatment vessel. In the first, the ballast water is offloaded from a ship to a storage barge of sufficient capacity to store all the ship""s ballast. This barge is subsequently brought alongside a treatment vessel, with the filters discussed earlier, and the water is discharged to the treatment vessel. In the second scenario, a treatment vessel is used which has the capacity to process water at the rate the ship is off-loading its ballast, thus eliminating the storage barge and handling required in the first scenario. This second method is preferred for its greater simplicity, but requires larger-sized treatment vessels.
In dredge water treatment operations, the treatment vessel is located directly adjacent to the dredging operation to permit the discharge of excess water into the treatment vessel or into a storage barge of sufficient capacity to store excess dredge waters, if needed, prior to discharge of the water to the treatment vessel.
In further embodiments for graywater or blackwater treatment operations, the treatment vessel or vessels are located at strategic locations either at port facilities or at designed stations where cruise or other vessels could offload their wastewaters into a storage vessel that is transported to the treatment vessel, or directly into the treatment vessel.